There are 25 US Post Offices in Bureau County serving a total of 35,998 residents equating to 1,440 residents per post office. It's estimated that approximately 57,457 packages are handled across the 25 county post offices annually. Bureau County is a county located in the U.S. state of Illinois. As of the 2010 census, the population was 34,978. Its county seat is Princeton. Bureau County is part of the Ottawa\u2013Peru, IL Micropolitan Statistical Area, which is also included in the Chicago\u2013Naperville, IL\u2013IN\u2013WI Combined Statistical Area. Hennepin Canal Parkway State Park is located partly in this county."